1. Field of Invention
The invention relates to an information embedding method and, in particular, to a method that embeds a binary watermark image into the subband image of an original image.
2. Related Art
It is a trend to digitize information nowdays. However, due to the ease of distributing and copying digital images, the protection is therefore not as easy as convention ones. The copyright of digital data thus receives much attention. To ensure the security of digital image data transmissions and to avoid malicious eavesdropping, a widely used method is the “watermark embedding technique”. The “watermark embedding technique” is to embed in an orignal digital image to be transmitted some watermark information that is unrelated to the original digital image data. Unauthorized third parties are thus unable to take and use the digital image data. Therefore, currently most digital image data use this way to prevent eavesdroppers from stealing and damaging the original digital image data.
From the appearance of the watermark printed digital image, one can simply categorize the watermark information as visible and invisible. From the operational processing, one can divide the watermark information into space domain and frequency domain. However, a good watermark embedding technique has to satisfy the following three basic properties in order to achieve the goal of protecting the original digital image data. First, it should be uneasy to detect. That is, the embedded watermark information should not be easy to be discovered by normal image processing methods. Alternatively, one can try to embed the watermark information in such a way that only a tiny change is made to the image and human eyes cannot detect the difference. Secondly, it has to be robust. The embedded watermark information should be able to resistant to various kinds of attacks, including image processing, magnification, shrinking, rotation, compression and modification. Thirdly, it does not require the original digital image data. When detecting or recovering the watermark information, one should not need another copy of the original digital image data in order to process.
Therefore, it is an important trend and direction for people in the field of watermark embedding detection technology to develop an effective and robust watermark embedding technique for all kinds of digital image data so that users can rapidly and easily detect the watermark information and recovering the original digital image.